Messages in this thread | | | Date | Sat, 13 Mar 2004 15:39:57 +0100 | From | Danjel McGougan <> | Subject | Re: [PATCH] ppc32 copy_to_user dcbt fixup |
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Bryan Rittmeyer wrote: > copy_tofrom_user and copy_page use dcbt to prefetch source data [1]. > Since at least 2.4.17, these functions have been prefetching > beyond the end of the source buffer, leading to two problems: > > 1. Subtly broken software cache coherency. If the area following src > was invalidate_dcache_range'd prior to submitting for DMA, > an out-of-bounds dcbt from copy_to_user of a separate slab object > may read in the area before DMA completion. When the DMA does complete, > data will not be loaded from RAM because stale data is already in cache. > Thus you get a corrupt network packet, bogus audio capture, etc. > [snip]
I am no expert on the ppc arch, but in my humble opinion it seems strange to invalidate the dcache *before* the memory-writing DMA-transaction. The obvious solution is to invalidate the dcache *after* DMA completion. It seems hard to guarantee that nobody will touch the memory area in question during the DMA.
Just some clue-less comments from a linux-kernel lurker.
Regards, Danjel - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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